Core Science · EN
Isotopes
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Their chemistry is very similar, while their masses and nuclear stability can differ.
Why scientists care
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Their chemistry is very similar, while their masses and nuclear stability can differ.
One element can therefore have several nuclear versions without changing its place in the periodic table.
A concrete example
Hydrogen-1 and deuterium are both hydrogen because each nucleus has one proton, but deuterium also has one neutron.
Try to notice
Science becomes memorable when a definition is connected to something measurable or observable.
The key idea
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Their chemistry is very similar, while their masses and nuclear stability can differ.
Why it matters
One element can therefore have several nuclear versions without changing its place in the periodic table.
Core idea
An element is defined by its proton count, not its neutron count. Two isotopes of the same element therefore share an atomic number but have different masses.
A concrete example
Natural chlorine contains mainly two isotopes. The periodic-table mass is an abundance-weighted average, not the mass of an imaginary chlorine atom.
Why it matters
This concept connects symbolic scientific language with what actually happens at atomic, molecular or experimental scales. Before applying a formula, always check the quantities, units and assumptions of the model.
Check it yourself
Restate the idea without technical vocabulary, then repeat the reasoning with a simple value. If your explanation and calculation tell different stories, revisit the assumptions.
Understand it before converting
Mass is not just a classroom quantity: it appears constantly in cooking, laboratories, transport, industry and science. Units are chosen for practical reasons. Some are convenient in everyday life, while others dominate scientific or technical work. This page deliberately focuses on familiar units — milligrams, grams, kilograms, tonnes, ounces and pounds — instead of presenting a long catalogue of rarely used formats. Every pair links to a dedicated conversion page with the calculation rule, worked examples and useful reference values. The aim is to get the answer quickly while still understanding what is being converted and whether the result makes physical sense.
Isotopes and average atomic mass